S u m m a r y :
Females have a harder time than males to gain weight, and the answer might be lying in their brains! Or so says a new study published in the journal Nature Communications.
Why do females have such a hard time gaining weight? This might seem like the wrong question (I mean, why should they put on weight anyway!) but past research has shown that when male and female mice consume the same high-fat diets, the female will not gain as much weight as the former. This sex difference remained a mystery to scientists—until now. The new research that has come up with a plausible explanation for this phenomenon was conducted by a team from Baylor College of Medicine. Otherwise, other scientists have come forth with possible reasons as to why males put up more weight: it might be because of the different sex chromosomes and sex hormones, but very little is actually known about these associations.
Senior study author, Dr Yong Xu, explains that their aim has been to identify a third factor that could be behind the sex differences in body weight regulation. The team has endeavoured to focus on the brain to gain a better understanding of its possible role in body weight control.
“We think ours is among the first studies looking at the brain to understand weight control differences between males and females,” says Xu.
Xu and his colleagues built up from previous research. For instance, given that earlier studies indicated that various neurone populations worked together to regulate weight, they wanted to find any difference in these populations between males and females.
“One of the most important functions of all neurons is firing electrical signals. That’s how neurons talk to each other and to other tissues,” Xu said. “We compared the firing rate of many types of neurons between males and females and found a few that fired differently. We focused on one type, called POMC neurons, located in the hypothalamus.”
POMC neurones help in the maintenance of normal body weight by responding to chronically high fat diets with a reduced appetite and greater energy expenditure, says senior author Dr. Chunmei Wang.
According to Wang, their findings show that female POMC neurones fire at a more rapid rate than those of males. What is behind this speed difference? Upon investigating further, Xu and his team found that the genes coding for these neurones are expressed differently between males and females: for instance, gene TAp63 is expressed more in the latter.
“We know from previous work that when we knock out the gene TAp63 in the entire body of a mouse, the animal becomes obese,” Xu said. “Here, we knocked out the gene only in POMC neurons and strikingly, this change did not affect male mice. On the other hand, female mice developed male-like obesity.”
Knocking out TAp63 influenced weight control in females, and it lowered the firing activity of the neurones to the same level as males’. Doing the same in males, though, did not impact on the firing rate.
So, it appears that female POMC neurones express greater levels of TAp63, causing a faster firing. Consequently, females have less appetite, and they spend more energy, which keeps them from gaining weight.
“We think that our findings suggest that, in addition to studying chromosome and hormonal differences between males and females, scientists should also pay attention to this third category of factors,” Xu said. “We hope our study will encourage other researchers to continue investigating this line of research.”